This application claims the benefit of the Korean Patent Application No. P2001-088544 filed on Dec. 29, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to an active matrix organic electroluminescence display (ELD) device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for increasing a luminance and securing a storage capacitance at the same time.
2. Discussion of the Related Art
As information technologies develop rapidly, a necessity for flat panel displays, which have advantages of thinness, light weight, and low power consumption, has been increased. Accordingly, various flat panel display devices, such as a liquid crystal display (LCD) device, a plasma display panel (PDP), a field emission display device, and an electroluminescence display (ELD) device, have been researched and developed. The electro-luminescence display (ELD) device makes use of an electro-luminescence phenomenon, in which light is generated when an electric field of a certain intensity is applied to a fluorescent substance.
The electroluminescence display (ELD) devices can be classified into an inorganic electroluminescence display (ELD) device and an organic electroluminescence display (ELD) device depending upon a source material for exciting carriers. The organic electroluminescence display (ELD) device has drawn attention as an efficient display device for natural colors because it can display all colors from the entire visible light range, and has a high brightness and a low driving voltage. In addition, because the organic electroluminescence display (ELD) device is self-luminescent, it has a high contrast ratio and is suitable for an ultra-thin type display device. Moreover, due to its simple manufacturing process, a level of environmental contamination may become relatively low. Besides, the organic electroluminescence display (ELD) device has a response time of only a few microseconds (xcexcs), so that it is suitable for displaying moving images. The organic electroluminescence display (ELD) device has no limit in a viewing angle and is stable at low temperature conditions. Because it is driven with a relatively low voltage in the range of about 5V and 15V, manufacturing and design of a driving circuit are easy.
A structure of the organic electroluminescence display (ELD) device is similar to that of the inorganic electroluminescence display (ELD) device, except for that a light-emitting principle is different from that of the inorganic electroluminescence display (ELD) device. More specifically, the organic electroluminescence display (ELD) device emits light on a recombination of an electron and a hole, and thus being referred to as an organic light emitting diode (OLED). Recently, an active matrix type, in which a plurality of pixels are arranged in a matrix form, and a thin film transistor is connected thereto, has been widely applied to the flat panel display devices. The active matrix type is also applied to the organic electro-luminescence display (ELD) device, which is referred to as an active matrix organic electroluminescence display (ELD) device.
FIG. 1 is a circuit diagram illustrating a pixel of a related art active matrix organic electroluminescence display device. As shown in FIG. 1, a pixel of the active matrix organic electro-luminescent display device has a switching thin film transistor 4, a driving thin film transistor 5, a storage capacitor 6, and a light emitting diode (LED) 7. The switching thin film transistor 4 and the driving thin film transistor 5 are formed of p-type polycrystalline silicon thin film transistors. A gate electrode of the switching thin film transistor 4 is connected to the gate line 1, and a source electrode is connected to the data line 2. A drain electrode of the switching thin film transistor 4 is connected to a gate electrode of the driving thin film transistor 5. A drain electrode of the driving thin film transistor 5 is connected to an anode electrode of the light emitting diode (LED) 7. A source electrode of the driving thin film transistor 5 is connected to a power line 3, and a cathode electrode of the light emitting diode (LED) 7 is grounded. A storage capacitor 6 is connected to the gate electrode and the source electrode of the driving thin film transistor 5.
When a signal is applied to the gate line 1, the switching thin film transistor 4 is turned on, and an image signal from the data line 2 is stored into the storage capacitor 6 through the switching thin film transistor 4. When the image signal is applied to the gate electrode of the driving thin film transistor 5, the driving thin film transistor 5 is turned on, thereby allowing the light emitting diode (LED) 7 to emit light. A luminance of the light emitting diode (LED) 7 is controlled by varying a current of the light emitting diode (LED) 7. The storage capacitor 6 keeps a gate voltage of the driving thin film transistor 5 constant even when the switching thin film transistor 4 is turned off. More specifically, since the driving thin film transistor 5 can be driven by a stored voltage in the storage capacitor 6, even when the switch thin film transistor is turned off, the electric current may continue to flow into the light emitting diode (LED) 7, therby allowing the light emitting diode (LED) to emit light until the next image signal comes in.
FIG. 2 is a plane view of the related art active matrix organic electroluminescence display (ELD) device. As shown in FIG. 2, a gate line 21 and a data line 22 cross each other and define a pixel region xe2x80x9cPxe2x80x9d. A switching thin film transistor TS is formed at each crossing point of the gate and data lines 21 and 22 and connected to the gate and data line 21 and 22. A driving thin film transistor TD, which is connected to the switching thin film transistor TS, is formed in the pixel region xe2x80x9cPxe2x80x9d. A gate electrode 41 of a driving thin film transistor TD is connected to a drain electrode 31 of a switching thin film transistor TS. A source electrode 42 of the driving thin film transistor TD is connected to a power line 51, which is parallel to the data line 22. A drain electrode 43 of the driving thin film transistor TD is formed in the pixel region xe2x80x9cPxe2x80x9d and connected to a pixel electrode 61, which is formed of a transparent conductive material. A first capacitor electrode 52, which is connected to the power line 51, is formed in the pixel region xe2x80x9cPxe2x80x9d. A second capacitor electrode 71 and 72 is formed of polycrystalline silicon and connected to the gate electrode 41 of the driving thin film transistor TD. The second capacitor electrode 71 and 72 overlaps the power line 51 and the first capacitor electrode 52 to form a storage capacitor.
However, since the power line 51 and the first capacitor electrode 52 are formed of an opaque metal material, in the above-described active matrix organic electroluminescence display device, an aperture ratio is decreased. Accordingly, an area of the storage capacitor in the pixel region xe2x80x9cPxe2x80x9d must be reduced in order to increase the aperture ratio. However, when the area of the storage capacitor is reduced, a storage capacitance of the storage capacitor is decreased, thereby increasing a kick-back voltage. In addition, a leakage of a signal cannot be prevented. Furthermore, in the related art active matrix organic electro-luminescence display (ELD) device, resistances of the power line are electrically connected in series, thereby resulting in a relatively high resistance. Accordingly, an image of low picture quality is displayed due to the heat generated by the high resistance of the power line. This problem becomes more serious as the active matrix organic electroluminescence display (ELD) device becomes larger in size.
Accordingly, the present invention is directed to an active matrix organic electroluminescence display (ELD) device and a method of fabricating the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
Another object of the present invention is to provide an active matrix organic electroluminescence display (ELD) device and a method of fabricating the same, in which a capacitor electrode is formed of a transparent conductive material to increase a luminance and secure a storage capacitance at the same time.
Another object of the present invention is to provide an active matrix organic electroluminescence display (ELD) device and a method of fabricating the same, in which power lines are connected to each other in parallel to reduce a total electrical resistance of the power line, thereby improving a picture quality of displayed images by preventing a heat generation caused by high resistance.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an active matrix organic electroluminescence display (ELD) device includes gate and data lines defining a pixel region on a substrate, a switching thin film transistor connected to the gate and data lines, a driving thin film transistor connected to the switching thin film transistor, a power line connected to the driving thin film transistor, a transparent first capacitor electrode connected to and overlapping the power line, a second capacitor electrode connected to the driving thin film transistor, and a pixel electrode formed at the pixel region and connected to the first driving thin film transistor.
Herein, the power line is formed of the same material as the first capacitor electrode. The first capacitor electrode is formed of one of indium tin oxide (ITO) and indium zinc oxide (IZO)
The active matrix organic electroluminescence display device further includes contact holes at the overlapped portion of the power line and the first capacitor electrode.
The power line may also be formed of an opaque metal material, and the first capacitor electrode may be formed of one of indium tin oxide (ITO) and indium zinc oxide (IZO). The second capacitor electrode is formed of doped polycrystalline silicon.
In another aspect of the present invention, an active matrix organic electroluminescence display (ELD) device includes gate and data lines defining a pixel region on a substrate, a switching thin film transistor connected to the gate and data lines, a driving thin film transistor connected to the switching thin film transistor, a power line connected to the driving thin film transistor and having first, second, and third portions, the first and second portions being parallel to the data line, the third portion connecting the first and second portions, the first portion being connected to the second portion of the power line of an adjacent pixel region, a first capacitor electrode connected to the first driving thin film transistor and overlapping the first portion of the power line, and a pixel electrode formed at the pixel region and connected to the first driving thin film transistor.
Herein, the second and third portions of the power line overlap edge portions of the pixel electrode. The power line is formed of a transparent conductive material. The power line may also be formed of one of indium tin oxide (ITO) and indium zinc oxide (IZO).
The active matrix organic electroluminescence display (ELD) device further includes a second capacitor electrode extended from the first portion of the power line to the pixel region, and a third capacitor electrode extended from the first capacitor electrode and overlapping the second capacitor electrode.
The second capacitor electrode may be formed of one of indium tin oxide (ITO) and indium zinc oxide (IZO), and the third capacitor electrode may be formed of doped polycrystalline silicon. The first capacitor electrode may also be formed of doped polycrystalline silicon.
In another aspect of the present invention, an active matrix organic electroluminescence display device includes gate and data lines defining a pixel region on a substrate, a first switching thin film transistor connected to the gate and data lines, a first driving thin film transistor connected to the first switching thin film transistor, a second switching thin film transistor connected to the first switching thin film transistor, a second driving thin film transistor connected to the second switching thin film transistor and the first driving thin film transistor, a power line connected to the first driving thin film transistor, a first capacitor electrode formed of a transparent conductive material on the pixel region and connected to the power line, a second capacitor electrode connected to the first driving thin film transistor and overlapping the first capacitor electrode, and a pixel electrode formed at the pixel region and connected to the first driving thin film transistor.
In another aspect of the present invention, an active matrix organic electroluminescence display device includes gate and data lines defining a pixel region on a substrate, a first switching thin film transistor connected to the gate and data lines, a first driving thin film transistor connected to the first switching thin film transistor, a second switching thin film transistor connected to the first switching thin film transistor, a second driving thin film transistor connected to the second switching thin film transistor and the first driving thin film transistor, a power line connected to the first driving thin film transistor and having first, second, and third portions, the first and second portions being parallel to the data line, the third portion connecting the first and second portions, the first portion being connected to the second portion of the power line of an adjacent pixel region, a first capacitor electrode connected to the first driving thin film transistor and overlapping the first portion of the power line, and a pixel electrode formed in the pixel region and connected to the first driving thin film transistor.
In another aspect of the present invention, a method of forming an active matrix organic electroluminescence display device includes forming gate and data lines defining a pixel region on a substrate, forming a switching thin film transistor connected to the gate and data lines, forming a driving thin film transistor connected to the switching thin film transistor, forming a power line connected to the driving thin film transistor, forming a transparent first capacitor electrode connected to and overlapping the power line, forming a second capacitor electrode connected to the driving thin film transistor, and forming a pixel electrode formed at the pixel region and connected to the driving thin film transistor.
In another aspect of the present invention, a method of forming an active matrix organic electroluminescence display device includes forming gate and data lines defining a pixel region on a substrate, forming a switching thin film transistor connected to the gate and data lines, forming a driving thin film transistor connected to the switching thin film transistor, forming a power line connected to the driving thin film transistor and having first, second, and third portions, the first and second portions being parallel to the data line, the third portion connecting the first and second portions, the first portion being connected to the second portion of the power line of an adjacent pixel region, forming a first capacitor electrode connected to the driving thin film transistor and overlapping the first portion of the power line, and forming a pixel electrode formed at the pixel region and connected to the driving thin film transistor.
In another aspect of the present invention, a method of forming an active matrix organic electroluminescence display device includes forming gate and data lines defining a pixel region on a substrate, forming a first switching thin film transistor connected to the gate and data lines, forming a first driving thin film transistor connected to the first switching thin film transistor, forming a second switching thin film transistor connected to the first switching thin film transistor, forming a second driving thin film transistor connected to the second switching thin film transistor and the first driving thin film transistor, forming a power line connected to the first driving thin film transistor, forming a first capacitor electrode formed of a transparent conductive material on the pixel region and connected to the power line, forming a second capacitor electrode connected to the first driving thin film transistor and overlapping the first capacitor electrode, and forming a pixel electrode formed at the pixel region and connected to the first driving thin film transistor.
In a further aspect of the present invention, a method of forming an active matrix organic electroluminescence display device includes forming gate and data lines defining a pixel region on a substrate, forming a first switching thin film transistor connected to the gate and data lines, forming a first driving thin film transistor connected to the first switching thin film transistor, forming a second switching thin film transistor connected to the first switching thin film transistor, forming a second driving thin film transistor connected to the second switching thin film transistor and the first driving thin film transistor, forming a power line connected to the first driving thin film transistor and having first, second, and third portions, the first and second portions being parallel to the data line, the third portion connecting the first and second portions, the first portion being connected to the second portion of the power line of an adjacent pixel region, forming a first capacitor electrode connected to the first driving thin film transistor and overlapping the first portion of the power line, and forming a pixel electrode formed in the pixel region and connected to the first driving thin film transistor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.